Biosecurity Queensland confirmed yesterday it had quarantined a property at Hervey Bay after test results from a deceased horse returned a positive result for Hendra.
The agency has also quarantined two adjoining properties in the Boondall area after test results from a deceased horse returned a positive result.
Queensland Chief Veterinary Officer, Dr Rick Symons, said the Boondall horse was euthanised on Friday.
"We will now be testing six more horses at this site," he said.
"These horses will be monitored daily over the next month."
The Boondall case followed confirmation that a horse euthanased at the Hervey Bay property on Wednesday also had Hendra.
In Queensland, there are now six separate locations where Biosecurity Queensland is managing the aftermath of cases - Beaudesert, Mt Alford, Park Ridge, Kuranda, Hervey Bay and Boondall.
Symons said a second horse on the Hervey Bay property is being checked.
He said it was very unusual to see so many cases cropping up in such a short period of time.
"It could be because of a heightened awareness of Hendra virus which is resulting in the high number of samples we are currently receiving for testing - up to five times as many samples for Hendra testing as we normally would," he said.
"There is clearly a heightened awareness among vets and horse owners about the possibility of Hendra virus infection when a horse becomes sick.
"Biosecurity Queensland and Queensland Health will continue to manage these cases and any others that may arise with our proven approach."
Standard procedures involves quarantining affected properties, tracing movements to identify any other horses at risk, daily monitoring of horses and human health assessments.
"At the same time we are working closely with New South Wales authorities as part of the recently-announced interstate Hendra virus taskforce, which includes research into how flying foxes transmit the disease to horses."
Queensland Health staff will undertake contact tracing work at the scenes of the two latest outbreaks to ensure all people potentially exposed to the sick horse have been identified.
Queensland chief health officer Dr Jeannette Young reassured the community that transmission of the virus required close contact with body fluids of the sick horse.
"There is no evidence the virus can be passed directly from flying fox [bats] to humans, from the environment to humans, from humans to horses, or can be transmitted by airborne droplets," Young said.
The virus, first identified in 1994, is carried by flying foxes and can be transmitted to horses, probably through accidentally ingesting droppings, urine or birth cleanings.
The virus is known to have jumped from horses to humans on seven occasions. Four of the victims died - the last two being equine veterinarians.